As is generally well known in the railway industry, the brake system used on the railway cars employs a plurality of force transmitting members to convert supply of the pneumatic fluid pressure from the brake pipe into a mechanical force to apply and bias one or more brake shoes against the tread of one or more wheels of the railway car.
When a single railway car or a plurality of railway cars are parked at a siding, or yard, the hand brake or parking brake on at least some of these railways cars is applied as a precaution against unwanted or unexpected movement of the cars. A typical railway car hand brake system normally consists of an apparatus for manually applying and biasing one or more brake shoes against the tread of one or more wheels of the railway car by either turning a hand wheel or pumping a ratchet handle on a hand brake mechanism attached to the railway car. However, it has been known for an operator to improperly apply the hand brake causing undesirable movement of the railway cars.
Furthermore, during an emergency brake application or during loss of the fluid pressure in the brake pipe due to rapture or disconnect, it is necessary to apply and maintain brakes until the supply of the fluid pressure can be restored.
Prior to the conception and design of the present invention, numerous attempts have been made to alleviate the operational problems related to parking individual railway cars. U.S. Pat. No. 7,140,477 issued to Engle et al., U.S. Pat. No. 6,854,570 issued to Connell, U.S. Pat. No. 6,761,253 issued to Kanjo et al., and U.S. Pat. No. 6,491,352 issued to Engle describe various constructions of the parking brake assemblies. However, there is a continuing need for a parking brake assembly for use in a railway vehicle braking system which applies brakes due to supply of air pressure or through a hand brake mechanism and which maintains brakes in the applied condition when the supply of air pressure is discontinued.